The present invention relates generally to video and graphics display devices, and more particularly to microdisplays using liquid crystal materials on silicon.
The technology of using liquid crystal materials in microdisplays is relatively new. The liquid crystal material, which forms the optical component of the microdisplay, is placed directly on top of a silicon integrated circuit, or pixel array, and the signals to turn the individual picture elements, or pixels, of the microdisplay on and off are generated on the silicon integrated circuit.
The term xe2x80x9cmicrodisplayxe2x80x9d is used since the display in a typical embodiment has an array of 1,024xc3x97768 pixels (the individual pixel size is approximately 12 xcexc) and the silicon die is about 1.3 cmxc3x971 cm in area.
The microdisplay works by having an illuminator, which converts non-polarized light from an ordinary light source into a polarized light beam onto the microdisplay. The microdisplay will reflect the light in a manner such that the plane of polarization of the light will or will not be rotated. The light then passes back to the illuminator which acts as an analyzer and causes the pixels to be bright or dark depending on whether the plane of polarization was rotated. Above the illuminator/analyzer are viewing optics which form the image.
Applications for these microdisplays continue to expand. In one application, they are used for viewfinders for digital cameras and camcorders. In another, two microdisplays are fixed to a frame, such as eyeglasses, thereby giving a user a virtual image of a virtual computer screen which is very lightweight and also very private.
Another application is in projection monitors for use in conference rooms. Since the microdisplay is reflective, high intensity light can be used to illuminate the microdisplay and, by using projection optics, an image of the microdisplay can be projected onto a large screen.
In the manufacturing process, the silicon die which contains the finished circuitry is sent through the following steps. An adhesive sealant ring, which will act to contain the liquid crystal material, is placed around the pixel array in a display area. Immediately after the ring is deposited, a conductively coated glass is placed on top of the ring thereby forming a chamber to hold the liquid crystal material. The coating on the glass is generally indium tin oxide (ITO) because it is highly conductive at thicknesses which render it transparent in the visible spectrum. The coating is on the surface of the glass in contact with the liquid crystal material and forms an electrically conductive, but transparent, common electrode. The common electrode forms the electrical cell which forms the image in conjunction with the display area and the liquid crystal material.
Following the adhesion of the coated glass on top of the silicon die by virtue of the adhesive sealant ring, the liquid crystal material is introduced into the space between the glass and the silicon die. Following this, a mechanical contact is made to the coated surface of the glass. The mechanical contact is necessary to provide the common electrode bias to the coated glass. The glass and the silicon die have to be physically offset so that a mechanical contact can be made to the coated surface of the glass by using a mechanical clip. This is a disadvantage in manufacturing because it makes it difficult to cleanly scribe and break off the silicon die from the silicon wafer on which the microdisplays are being manufactured in volume. Following the separation into an individual microdisplay device, the microdisplay is placed in a display-utilizing device and bonding wires are connected to the bonding pads from the display-utilizing device.
Even more recently, microdisplays have been made where light emitting diodes are deposited on top of the pixel array in place of the liquid crystal material. This emissive display also has the same problematic requirement for a transparent common electrode. Since these microdisplays are made in tremendous volumes, even slight cost reductions result in savings of significant sums of money. Thus, there is a continuous struggle to reduce costs and simplify manufacturing.
The present invention provides a microdisplay in which a display area, a bonding pad connected to the display area, and a contact pad operatively connected to the bonding pad are all located on a silicon die. An electrically conductive, coated glass is located over the display area and is electrically connected to the contact pad by a flexible conductive material. This approach eliminates a mechanical contact clip and allows the coated glass to be flush with the scribe and break line of the silicon die which was required with the prior art microdisplay. Under the coated glass is a material which responds to electricity to control the transmission or emission of light.
The present invention further provides a microdisplay that has the circuitry located on the silicon die necessary to generate the common electrode bias to drive the electrically coated glass portion of the microdisplay. Thus, the common electrode bias generator no longer needs to be on or in a separate component from the microdisplay. The contact between the common electrode bias generator and the electrical coating is made by a contact pad and a flexible electrical conductor. This promotes greater integration at the microdisplay.
The present invention further provides a microdisplay which eliminates the need for mechanical fasteners, and also the need to have a glass overhang which interferes with separation of the silicon die from the silicon wafer in which it is processed.
The above and additional advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description when taken in conjunction with the accompanying drawings.